Wormhole

A wormhole is a conduit in space that connects two points of space-time together through subspace. A wormhole has a mouth at each end of the conduit that allows anything to travel through it. If a large enough, or stable enough wormhole is found then starships can pass through the wormhole and travel a great distance in relatively little time.

Studies showed that in order for the construction of an artificial wormhole to be possible, one would be required to construct a Verteron collider of at least eight kilometers in length. Another notable problem was not the size of the machinery involved but instead was the exotic construction material needed in order to create a permanent site. The mouth of an artificial wormhole with its outward radial pressure had tremendous tidal tension which was similar to the center of a massive neutron star. Thus, any building material would need to stand up to that kind of pressure for the wormhole to continue being stable. (DS9novel: Behind Enemy Lines)

The ancient Furies who were banished to the Delta Quadrant had the knowledge to create an artificial wormhole by destroying their star which created a subspace explosion that produced a shortly-lived but stable wormhole across quadrants. (VOYnovel: The Final Fury)